Std. 11 Physics Revision
Units , Measurements and Dimensions # System of Measurements : SI(System International) , MKS(metre-kilogram-seconds) , CGS(centimetre-gram-seconds) , FPS(foot-pound-seconds) # Fundamental Units : Mass(kg) , Length(m) , Time(s) , Temperature(K) , Current(I) , Luminous Intensity(cd) , Amount of Substance(mol) . Derived Units : The units that depnd upon fundamental units . e.g. veloity (ms-1) depends on length and time . # Methods of Measurements : '''For measuring distance of stars , planets , we use the parallax method . For determining mass of planets , we use gravitational methods . For the measurement of masses of atomic species , mass spectrographs are used . For accurate measurement of time , we use atomic clocks based on the vibrations produced in a Cesium - 133 atom . # '''Dimensional Analysis : '''Dimensional Analysis deals with the powers to which the unit of a physical quantity is raised to . e.g. dimensions of velocity (ms-1) is L1M0T-1 (only fundamental units to be used) . # '''Uses of Dimensional Analysis : ## To check the correctness of an equation (Find the dimensions of LHS and RHS ) ## To find the conversion factor (Convert the units individually to find over-all conversion factor ) ## To find the dimensions by comparison method (Find Dimensions of the LHS and equate with RHS) # Significant Figures : '''In order to understand significant figures , we must try to understand and accept that no measurement can be accurate . ## For example , when the Least count of a measuring instrument is 0.01 m , it will give us accurate readings up to 0.01 m only , measurements smaller than 0.01 m cannot be measured by it . This means that no matter how small the least count of the measuring instrument is , there will always be an error of order one less up to 10-∞ . ## Thus , we need to decide the accuracy , which is enough to give a good idea of the quantity . For example , a person's height is 1.62 m ; but the measurement is accurate only up to 3 digits or 3 significant figures . The actual height could be 1.61927457634752641 m (even this would have an error beyond least count) .But 3 digits is enough to give a good amount of idea about a person's height . Thus , we measure it with 3 significant figures . # '''Order of Magnitude : Order of Magnitude is the power to which 10 is raised to ; to indicate the size of the quantity . #Errors ##'Personal Error :' Error occurring due to human errors . ##'Random Error :' Error occurring due to random changes in the environment of the experiment . ##'Systematic Error :' Error occurring due to a constant error in the readings of instrument . This is caused due to the faulty calibration of instrument . ##'Instrumental Error :' Error occurring due to faulty construction of instrument . # Error Analysis : ## Mean Value : Average of All readings ## Absolute Error : (Individual Readings) - (Mean Value) ## Mean Absolute Error : Average of all Absolute errors ## Relative Error : ( Mean Absolute Error) / (Mean Value) ## Percentage Error : ( Relative Error) x 100 # Error Calculation : ## If xn , then Error in x is multiplied by n ## The errors in the measurement of two quantities are added when the two quantities are multiplied or divied . If xy or x/y ; then add the errors in x and y . ## If the quantities are added or subtracted , then the errors in x and y are added . Scalars and Vectors # Scalar Quantities can be denoted by a number and a unit , i.e. Magnitude . Vector Quantities are denoted by magnitude and direction . # Types of Vectors : ## Equal Vectors : 'Vectors having same direction and magnitude . ## '''Parallel Vectors : '''Vectors having same direction ## '''Anti-Parallel Vectors : '''Vectors having opposite directions . ## '''Position Vector : '''Vector drawn from the origin to a point . ## '''Zero Vector : '''Vector of magnitude zero . ## '''Free Vector : '''Vector which can be moved through space , without changing it's direction . # '''Triangle Law : '''If two vectors exist such that their directions are taken in order , then their resultant is equal to the third of the triangle formed ; & the direction is from head of first to tail of second . # '''Parallelogram Law : '''The parallelogram law of Vectors states that if two vectors originate or meet at a common point , then their resultant is given by the diagonal of parallelogram formed . # '''Unit Vector : '''A unit vector has unit magnitude and any direction . If we divide a vector by it's magnitude , we get an unit vector . # '''Resolution of Vectors : '''for co-ordinate system , we know that ': x = rcosθ y = rsinθ . This is resolution of vector r . # Scalar Product : 'a.b = abcosθ # '''Vector Prodct : '''axb = absinθ Projectile Motion # Displacement is the change in position of an object with respect to a certain coordinate system or frame of reference . # Sped : ## Average Speed : The average speed in a time interval . ## Instantaneous Speed : The speed of a particle at a certain point in time . # Velocity is the rate of change of position of an object with respect to a specific co-ordinate system or frame of reference . ## Average Velocity : The average velocity in a time interval . ## Instantaneous Velocity : The velocity of a particle at a certain point in time . # The rate of change of velocity with respect to time is called as acceleration . Zero acceleration means uniform velocity . Positive acceleration means the velocity is increasing . Negative acceleration means velocity is decreasing . ## Average acceleration : The average acceleration in a time interval ## Instantaneous acceleration : The acceleration of a particle at a certain point in time . # Momentum is the Product of Mass and Velocity . p = mv # The rate of change of momentum with respect to time is called Force . It can also be formulated by Mass x Acceleration . F = ma . # '''Kinematical Equations : ' ## v = u + at ## s = ut + 1/2 at2 ## v2 = u2 + 2as # '''Relative Velocity : ## In the same direction ; a - b ## In opposite directions ; a + b ## If inclined at an angle θ , then ; Relative Velocity = sqrt ( a2 + b2 - 2abcosθ) # Force Friciton in Solids and Liquids Sound Waves Thermal Expansion Refraction Ray Optics Electrostatics Current Electricity Magnetic Effect of Electric Current Magnetism Electromagnetic Waves Most Important Questions Do study these for your final Exams . # Category:Physics Revision